Survey dangerous areas without entering them! Reduce on-site risks for civil engineering supervisors with LRTK

Construction sites often include areas that are dangerous for personnel to enter, such as steep slopes, swollen rivers, and landslide zones. Nevertheless, surveying such locations is indispensable for construction planning and as-built management. As a civil engineering supervisor, performing accurate surveys while ensuring worker safety is a major challenge. This article organizes the entry risks to dangerous areas on site and considers the difficulty of balancing safety management with surveying tasks. It also explains a contactless surveying method using the latest technology, LRTK, and introduces its effects on survey accuracy, work efficiency, and safety improvement. Finally, it touches on the advantages of cloud sharing and remote verification for risk management and summarizes the surveying safety reform enabled by LRTK.

Dangerous areas on site and entry risks

On civil engineering sites, there are many areas where workers face significant danger simply by entering. Typical examples include the following cases:

• Steep slopes and cut faces: On steep, unstable slopes there is a risk of falling or slipping during surveying. On faces that may collapse, the risk of secondary disasters such as falling rocks or ground collapse is high, and approaching them can be life-threatening.

• Riverbeds and swollen rivers: Surveying in riverbeds or rivers with increased flow after heavy rain carries the risk of slipping, falling, or being swept away by turbid currents. Riverbanks may collapse, so approaching survey points can be extremely dangerous.

• Landslide and collapse sites: Immediately after debris flows or landslides, the terrain is greatly deformed and the ground is loosened. Surveying amid scattered debris and fallen trees can lead to incidents such as being caught in collapsing footholds or slips. There is also the risk of secondary disasters from aftershocks or rainfall, so casual entry is prohibited.

There have been reported accidents in which surveyors fell along with collapsing footing on steep slopes or were swept away and killed during river surveys. In such hazardous locations, stringent safety measures during surveying (installation of lifelines, use of safety harnesses, placement of watchers, etc.) are required, but it is still difficult to eliminate all risks. The reality is that surveying dangerous areas is always conducted side by side with life-threatening risk.

The difficulty for civil engineering supervisors of balancing safety management and surveying tasks

Civil engineering supervisors are both the site safety managers and responsible for surveying as part of schedule and quality control. When surveying hazardous areas, they must obtain necessary data while prioritizing worker safety. However, if safety is prioritized to the point that sufficient surveying cannot be performed, construction planning accuracy and as-built verification suffer. Conversely, forcing personnel into dangerous areas increases the likelihood of accidents and could expose the supervisor to liability. Balancing safety and survey accuracy has become a dilemma that troubles site managers.

For example, when measuring the height of a steep cut face, the conventional method involved a worker ascending the slope with a safety rope, placing a staff (rod), and observing from below with a total station. Even with fall prevention measures, this method always exposed workers to danger. After a landslide, slopes are unstable and it is difficult for people to measure in detail. Traditionally, surveys were sometimes limited to safe areas outside the collapse, with unmeasured parts estimated. However, estimates have accuracy limits and can lead to errors in removed earth volume or missed additional countermeasures. For civil engineering supervisors who are required to ensure safety and perform accurate surveys, measuring dangerous areas has been a major challenge.

Conventional responses to this problem have included minimizing surveying at hazardous locations or outsourcing to specialist survey firms using drone photogrammetry or terrestrial laser scanning. Drone photogrammetry is indeed an effective method to capture data from the air without personnel entering the site. However, drone operation requires qualifications and flight permissions and is weather-dependent, so it cannot always be used casually. Outsourcing also has cost and scheduling constraints. As a result, sites have often had no choice but to rely on manual surveying despite the dangers.

Contactless surveying technology using LRTK

Recently, a contactless surveying method using LRTK has emerged as a way to resolve this dilemma. LRTK is a compact, high-precision RTK positioning solution developed by a startup from Tokyo Institute of Technology. RTK (Real Time Kinematic) is a technology that achieves centimeter-level positioning by applying real-time corrections to satellite positioning errors, and LRTK condenses RTK functionality into a pocket-sized device. It is designed to be attached to a smartphone or tablet and is compact, weighing approximately 125 g, with a thickness of about 1.3 cm (0.5 in). Unlike conventional RTK-GNSS receivers, there is no need to set up a tripod; simply attach it to your smartphone when needed to obtain high-precision positioning immediately. Positioning results can be checked in real time on the smartphone screen, and through a dedicated app it can be used for 3D point cloud measurement and layout (staking) work.

LRTK’s key feature is the combination of ease of use and high accuracy. GNSS standalone positioning typically has errors on the order of a few meters, but using LRTK yields horizontal and vertical errors of a few centimeters or less. On-site verification has reported positioning errors of less than 1 cm (0.4 in) when using LRTK, achieving accuracy comparable to conventional optical surveying instruments. It also supports Japan’s quasi-zenith satellite Michibiki’s centimeter-class augmentation service (CLAS), so even in mountainous areas or disaster sites where communication infrastructure is disrupted, correction information can be received directly from satellites to continue high-precision positioning. By using multiple satellite constellations (GPS, GLONASS, Galileo, Michibiki, etc.), stable positioning solutions can be obtained even in urban canyons or forested areas. With these technical measures, LRTK achieves professional surveying accuracy while offering portability and cost-effectiveness.

Contactless measurement by photogrammetry and 3D scanning

By utilizing LRTK, it is possible to perform photogrammetry and 3D scanning without entering hazardous areas. Using a smartphone camera or LiDAR sensor, you can capture the target from various angles to generate detailed three-dimensional models (point cloud data). For example, steep cut faces that were previously difficult to secure survey points for can be scanned from a safe distance simply by pointing and walking with a smartphone camera, producing a 3D representation of the entire face in a short time. Even for slopes on the order of 100 m (328.1 ft), high-density point clouds numbering tens of thousands of points can be acquired in a scan taking only a few minutes, allowing detailed understanding of surface irregularities. Heights and slopes at the top of faces that are difficult to measure can also be automatically calculated from the acquired point cloud data.

Point cloud data obtained from such contactless photogrammetry are tied to global coordinates (geodetic coordinates), making it easy to align with known site control points and design drawings. Orthoimages (composite overhead views) and contour maps generated from the photos can also be created with high accuracy, enabling assessment of items that were difficult to measure by conventional methods. Note that photogrammetry and laser scanning as methods for as-built management are formally recognized measurement methods under the Ministry of Land, Infrastructure, Transport and Tourism’s “As-Built Management Guidelines.” In other words, data obtained by LRTK and smartphone 3D measurement have sufficient reliability to be used for official as-built quantity calculations and quality inspections.

Three-dimensional surveying, which previously required expensive dedicated equipment and specialist technicians, has been transformed by LRTK. With the easy combination of a smartphone and a small device, anyone can quickly acquire detailed current-condition data, eliminating the need to risk approaching points one by one. This is truly “surveying by photographing the subject from a distance.”

Securing safe distances using AR technology

LRTK-compatible apps also incorporate AR (augmented reality) technology, which contributes to safety. With AR features, virtual survey information and design data can be overlaid on the real-world view through the smartphone screen. For example, you can acquire coordinates of targets (rocks or survey points) on a dangerous slope by tapping their positions through the camera from a distance, without going directly to measure them. Because high-precision RTK coordinates provide the base, the target positions displayed in AR align with the real objects, enabling reliable measurements from afar.

AR is also powerful in improving the efficiency of layout (staking) tasks. The LRTK app’s “coordinate navigation” function displays markers for set target coordinates on the AR screen and guides the user to those points. Using this, tasks that traditionally required two-person teams for setting batter boards or confirming structure locations can be done safely by one person. For example, in road construction staking, a surveyor can walk the site alone with a smartphone and place posts following AR-displayed markers. There is no need for a second person to enter a hazardous area to set up or guide survey equipment, resulting in large reductions in time and manpower.

AR can also be applied to remote verification of construction progress and as-built conditions. By projecting a 3D model of the design onto site imagery, you can remotely check whether excavation or embankment conforms to the design. For example, in steep slope finishing works, displaying the planned finish line in AR and observing the completed slope from a safe distance allows confirmation of any under- or over-excavation without approaching the cliff edge. In this way, AR functions not only as a measuring tool but also as a verification and guidance tool, ultimately reducing the frequency of personnel entering hazardous areas.

Effects on survey accuracy, work time, safety, and labor savings

Introducing contactless surveying with LRTK on-site can provide civil engineering supervisors with the following effects:

• Improved survey accuracy: With GNSS real-time corrections and advanced sensors, survey points can be recorded at centimeter-level accuracy. Digital measurement reduces reading errors and recording mistakes common in manual surveys, dramatically improving the accuracy of as-built dimensions. Complex terrain can be fully recorded with high-density point clouds, reducing re-surveying effort and the risk of design errors.

• Shortened work time: Using photography and scanning allows wide-area measurement at once, significantly reducing surveying time compared to conventional point-by-point methods. Because position coordinates are available in real time, data can be used immediately after measurement on site, cutting post-processing and drawing preparation time. In some cases, surveying can be completed in a fraction of the time required by traditional methods.

• Enhanced safety: The greatest benefit is reduced accident risk. By eliminating the need for personnel to enter dangerous areas, occupational hazards such as falls, collapses, and drowning can be prevented. Near-miss incidents associated with surveying are also reduced, enabling safety management that can lead to zero incidents.

• Labor savings: Lightweight smartphone-mounted equipment allows one person to perform surveys, reducing required personnel. Tasks that formerly needed two to three people can be done by one, enabling more effective use of limited human resources on construction sites facing manpower shortages. In addition, reduced heavy equipment transport and physical labor in hazardous areas lessens worker burden and reduces the load on experienced technicians.

Cloud sharing and remote verification support overall risk management

LRTK solutions also provide mechanisms to share survey data in the cloud in real time. Point cloud data and photos measured in the field can be uploaded to a dedicated cloud platform with a single tap. Office PCs can immediately view on-site survey results, eliminating the need for repeated trips to dangerous areas. For example, once the surveyor uploads the scanned slope data to the cloud, engineers or supervisors in the office can check the 3D model and promptly instruct where additional measurements or precautions are needed.

On the cloud, shared point clouds and survey points can be displayed on maps, and distance, area, and volume calculations can be performed. Because all stakeholders can discuss while viewing the same data, rework and oversights are reduced and risk countermeasure planning proceeds smoothly. In disaster response situations in particular, it is possible to keep on-site personnel to a minimum while remotely assessing conditions and planning recovery, yielding major benefits in both safety and time.

Storing data in the cloud also prevents loss of survey data if devices are damaged or lost on site. Keeping daily survey records in time series helps manage construction progress and monitor changes. Sharing data with remote branches or clients accelerates decision-making. In these ways, cloud sharing and remote verification strongly support overall on-site risk management.

Conclusion: LRTK’s surveying safety reform

LRTK offers a revolutionary solution to the long-standing challenge of surveying in hazardous sites. The idea that “dangerous areas can be surveyed without entering them” represents a true surveying safety reform that can drastically reduce on-site risks for civil engineering supervisors. When non-contact, high-precision surveying is realized, safety and efficiency are no longer a trade-off but achievable simultaneously. Reports from sites that have adopted LRTK indicate not only zero survey-related accidents but also overall productivity improvements and promotion of DX (digital transformation).

In the future construction industry, ensuring safety while leveraging advanced technologies will be indispensable. By proactively adopting cutting-edge tools like LRTK, the way hazardous surveying is performed is changing dramatically. As civil engineering supervisors, it is important to skillfully utilize these innovative tools to create work environments where everyone on site can work with peace of mind. Aiming for zero-risk surveying, the use of LRTK to balance on-site safety management and operational efficiency is poised to become the new standard.